If there is power to it then the suspect list does not include Junction boxes
(Well it might)
The suspect list
Prime: whatever you are plugging in (No longer functional)
secondary: The outlet itself (Rv Outlets are basically junk in my opinion)
TO test
first obtain a volt meter. one of the plug in meters like CW et-al sells or a Kill-a-watt. NOTE I really like the Kill-a-watt about a Kilobuck worth of meters in a 20 dollar box.
Plug it in and see if there is a reading. IF so good
plug in a lamp 100 watt incandascent and now look at the voltage and current readings. Should be 120 volt and just under 1 amp. power factor should be 1.0
This is a good outlet
if the voltage goes way down or even dark.. Bad connection Most likely AT THE OUTLET.